How do identify ECG leads?

Which one of the ECG 12 lead correspond to ECG in SHHS1 Database?

How does 2 snap electrodes measure 2 ECG Leads in MrOS?

Which ECG 12 leads correspond to ECG R and ECG L in MrOS Database?

Relevant information:

ECG Placement: Medtronic Medclear ECG snap electrodes. 2 leads place R subclavicle-L lower rib. Occasional modesty issues necessitated altering placement to right subclavicle-left suubclavicle. Position 3-5 cm below the middle of the right and left collar bones, in spaces between rib bones.

[White (-) electrode 3-5 cm.(2 finger breadths) below midpoint of right clavicle. Red (+) electrode is below the left ribcage

1. Prepare the marked sites by lightly abrading with prep gel. Remove excess prep gel before placing the electrode. Remove backing from electrode and place gel electrode on cleansed sites, with gel side down.
2. Snap electrode to lead wire before applying to subject’s skin, unless you have offset snaps.
3. Form a small "stress" loop with the wire immediately feeding the electrode, secure with a small amount of tape] (https://sleepdata.org/datasets/mros/files/m/browser/documentation/MrOS_Visit1_PSG_Manual_of_Procedures.pdf , Page 13 of 32, bottom right picture )

The SHHS 12-lead ECG was a separate test (done at rest, in clinic) from the ECG signal from the overnight sleep monitoring.

I'll ping someone else on the team regarding your other ECG lead questions.

The ECG in SHHS1 is a modified lead II. In MrOs there are two electrodes which collect their own signal. One can reference ECG R to ECG L to obtain a modified Lead II signal.